Partial versus total conductance histograms: A tool to identify magnetic effects in nanocontacs

Conductance histograms, a powerful tool to study transport properties of metallic nanocontacs, are analyzed from a new point of view. For Ni and Cu nanocontacs at room temperature, histograms obtained with no curve selection criteria are basically unaffected by the presence of a magnetic field. On the other hand, selection of particular sets of conductance curves indicates that conductance quantization could occur in steps of 12G0=e2/h and G0=2e2/h in Ni as well as in Cu in the presence or absence of a magnetic field. For Ni, the number of curves which exhibit plateaus at just G0 almost disappears with the applied field, indicating that magnetic fields are noticeable. On the contrary, for Cu nanocontacts, the analysis of partial conductance histograms reveals that the presence of an applied magnetic field keeps the ratio of curves that present plateaus at 12G0 with respect those presenting G0 plateaus unchanged. This would imply that the origin of the fractional quantization is not related to the presence of an intrinsic magnetic behavior of the Cu nanocontacs.